The present invention relates to a control signal generation circuit used in a wireless remote control signal transmitter for controlling the circuit operation of an instrument such as a television receiver, a video tape recorder, a toy, an air condisioner, etc., and more particularly to a custom code generation circuit employed in such a signal transmitter, which generates a custom code used for selecting and designating the instrument to be controlled among various ones.
A remote control signal transmitter generates a data code for controlling the operation of a controlled instrument in response to actuated or operated key or keys, wherein a semiconductor integrated circuit device (called hereinafter as an "IC") is widely used to form the data code responsive to the operated key and modulate the data code to transmit it by means of infrared rays, electromagnetic waves or supersonic waves. The remote control signal transmitter also generates a custom code in addition to the generation of the data code, the custom code being alloted to the instrument to be controlled in order that only that instrument responds to the code data. By the custom code, undesired instruments are prevented from responding to the data code.
Due to the increase in the remote-controlled instruments, a large number of custom codes should be formed. If a private remote control IC is manufactured with its peculiar custom code, its cost would be increased considerably. In order to solve this problem, it is required to generate a large number of custom codes by use of one kind remote control IC.
For this purpose, in prior art, a custom code setting terminal (called hereinafter as a "CCS" terminal) is provided to the remote control IC and key scan signals outputted from key scan output terminals are supplied selectively to the CCS terminal to obtain a custom code, as disclosed in U.S. Pat. No. 4,412,218. More specifically, the scan signals are outputted cyclically from the key scan output terminals to detect the operated key. Therefore, by coupling the selected key scan output terminal or terminals to the CCS terminal and detecting the level at the CCS terminal in synchronism with the generation timing of the scan signals, a pulse train having the combination of the data "1" and "0" is obtained. The custom code is derived from the pulse train. When the key scan output terminal or terminals coupled to the CCS terminal are changed and/or their numbers are increased or decreased, the combination of the data "1" and "0" is varied. The custom code is thus changed. Assuming that the remote control IC has eight key scan output terminals, 2.sup.8 (=256) kinds of the custom codes are obtained.
Thus, according to the art disclosed in the above document, various kinds of custom codes are produced by one type remote control IC which is manufactured at a low cost.
However, such a remote control IC requires a CCS terminal. An IC having a smaller number of external terminals is manufactured more cheaply, resulting in decreasing the cost of a signal transmitter. Even if a remote control IC has a large number of external terminals sufficiently to provide a CCS terminal, by replacing the CCS terminal with a key scan output terminal or a key input terminal, the number of key switches is increased, so that the remote control having various functions is carried out.